fix #555 detect mysqli

Detects if mysqli is present

layouts/v7/modules/Install/Step4.tpl

@@ -37,7 +37,11 @@
<td>{vtranslate('LBL_DATABASE_TYPE', 'Install')}<span class="no">*</span></td>
<td>
{vtranslate('MySQL', 'Install')}
-									<input type="hidden" value="mysql" name="db_type">
+									{if function_exists('mysqli_connect')}
+										<input type="hidden" value="mysqli" name="db_type">
+									{else}
+										<input type="hidden" value="mysql" name="db_type">
+									{/if}
</td>
</tr>
<tr>